Function‐based modulation control for modular multilevel converters under varying loading and parameters conditions

Abstract

This paper presents a new function-based modulation control technique for modular multilevel converters (MMC). The main contribution of the study is the formulation of two new modulation functions for the required switching signals of the MMC's upper and lower submodules respectively. The output and circulating current equations of the converter are employed to attain the arm's currents which are utilized for the proposed modulation functions, which have two important features: i) it is much less complex compared to the existing control methods of MMC; and ii) the proposed controller can be regulated properly to deal with parameter variations in a bid to ensure stable and accurate performance. In this controller, the MMC output current magnitude and phase angle required for special active and reactive power sharing can be easily applied to the modulation functions. Also, the equivalent capacitors of upper and lower sub-modules are discussed based on the proposed modulation functions. Finally, simulations are performed in Matlab/Simulink environment to evaluate the performance of the proposed control technique in both the dynamic conditions of load as well as varying parameters.

Research on Unbalance Fault-Tolerant Control Strategy of Modular Multilevel Photovoltaic Grid-Connected Inverter

“…When the upper arm of phase A has a SM failure, the carrier phase shift angle is changed to 2π/4, and the reference voltage of the SM of the upper arm is set to 814/4 = 203.5 V. The carrier phase shift angle of the lower arm is maintained at 2π/5, and the reference voltage of each SM is changed to 182 V according to Equation (16). The carrier phase shift angle of the non-fault phases and the reference voltage of the SM do not change.…”

“…The variation of upper and lower bridge legs SM output voltage ∆u cp_a (t), ∆u cn_a (t) can be written as Equations (16) and (17). …”

“…Lots of research has been conducted to find effective control methods for MMC topology [5][6][7]16,17]. Reference [5] proposes a control method based on a dynamic model, where six independent dynamical state variables are considered for effectively attaining the switching state functions of MMCs, as well as for an accurate control of the circulating currents.…”

“…On basis of this, a multi-loop control strategy based on a six-order dynamic model of the modular multilevel converter is presented [6], and the MMC is well controlled during normal operation. Besides, novel modulation function-based control strategies are proposed in [7,16], and the complexity of the control system is lowered to a large extent, compared with traditional control methods. Reference [17] further proposed a novel control strategy for MMC based on differential flatness theory, to guarantee the stable operation of the MMC against the input disturbance, model errors, and system uncertainties.…”

A Novel Protection and Location Scheme for Pole-to-Pole Fault in MMC-MVDC Distribution Grid

“…Therefore, when the fault occurs at f 1 , both sides feed current to the fault point. According to the specified positive direction, the current fault component detected by R 13 and R 14 should have the same polarity.…”